(Beyond Pesticides, October 8, 2013) Stress brought about by chronic exposure to sublethal levels of neonicotinoid pesticides causes bee colony failure, according to a new study published in the journal Ecology Letters. Scientists at Royal Holloway University of London have determined that low-level exposure to the pesticide imidacloprid at levels bees encounter in the field causes subtle impacts on individual bees that eventually cause colonies to collapse. This breakthrough study underlines repeated U.S. beekeeper and environmental group callsÂ for the Environmental Protection Agency (EPA) toÂ suspend the use of neonicotinoid pesticides, as the European Commission recently decided this past April.

Since 2006, honey bees and other pollinators in the U.S. and throughout the world have incurred ongoing and rapid population declines from hive abandonment and bee die-off in a phenomenon known as colony collapse disorder (CCD). Studies continue to link a class of systemic pesticides called neonicotinoids to the CCD phenomenon and pollinator decline in general. While scientists have cited multiple chemical and other factors that contribute to degrading bee health, until now no study has shown the internal mechanism within bee colonies that causes collapse. By focusing on chronic sublethal stressors, Royal Holloway researchers have addressed the complexities thatÂ contribute to colony losses.

In the study, scientists focus on colony level dynamics and the impact of pesticides on birth and death rates within bee colonies. Based on a biological phenomenon called the Allee effect, which attributes a positive correlation between population size or density and the mean individual fitness of a species or population, researchers found that two bee colonies exposed to the same stressors can have very different fates. In other words, a bee colonyâ€™s resiliency and survival can be significantly impacted by stressors at earlier points in the colonyâ€™s life cycle. Chronic stressors (over several weeks) such as pesticides, not excluding disease, parasites, and habitat loss, can result in feedback on the birth and death rates of the colony, and eventually cause collapse. Lead author John Bryden, Ph.D, explains, â€śExposing bees to pesticides is a bit like adding more and more weight on someoneâ€™s shoulders. A person can keep walking normally under a bit of weight, but when it gets too much â€“ they collapse. Similarly, bee colonies can keep growing when bees arenâ€™t too stressed, but if stress levels get too high the colony will eventually fail.â€ť

Numerous studies have examined the impacts of pesticides on bees at the colony level. A USDA funded study published in July 2013 found that exposure to the vast array of chemical combinations found in honey bee hives can weaken beeâ€™s immune systems and make them more susceptible to parasites and other pathogens. Studies published in March 2013 found that neonicotinoid pesticides impact beeâ€™s learning and memory, making it more difficult for bees to forage and find food. While itâ€™s certain that numerous stressors are acting upon bees, as evidenced by a recent study linking exhaust fumes to impairment of beeâ€™s ability to find food, the evidence continues to implicate pesticides as critical components of the CCD phenomenon. In fact, before the neonicotinoid pesticide clothianidin was allowed on to the market, an internal EPA document cited the agencyâ€™s honey bee colony level field study as inadequate. The agency registered the pesticide â€śconditionally,â€ť despite concerns about its impact on domestic honey bees and other pollinators.

In response, Beyond Pesticides has worked with allies, including beekeepers and environmental groups, to force EPA expedite a response to the pollinator crisis through legal petitions and declare the pesticide clothianidin an â€śimminent hazardâ€ť to honey bees. After EPA rebuffed the legal petition, the coalition filed a lawsuit in Federal District Court against the agency for its failure to adequately protect pollinators. The lawsuit seeks the suspension of the registrations of the neonicotiniods clothianidin and thiamethoxam, which have repeatedly been identified as highly toxic to honey bees, the clear cause of major bee kills, and a significant contributor to the devastating ongoing mortality of bees. The suit challenges EPAâ€™s oversight of bee-killing pesticides, as well as the agencyâ€™s practice of â€śconditional registrationâ€ť and labeling deficiencies.

As co-author of the Royal Holloway study, Nigel Raine, Ph.D explains, â€śPesticides can have a detrimental effect on bees at levels used in the field. Our research will provide important evidence for policymakers. The way we test pesticides, the way we assess their impact on bees, and the way we manage pesticides can all be improved.â€ť With one in three bites of food reliant on bees and other beneficial species for pollination, the decline of pollinators requires swift action. In the absence long overdue protections, Beyond Pesticides is promoting a multi-faceted strategy that focuses on a precautionary approach to our pollinator crisis.

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